Retrofocus type wide angle objective lens



April 1970 IKUO MORI 3, 07,559

RETROFOCUS TYPE WIDE ANGLE OBJECTIVE LENS Filed Dec. 1. 1966 3 Sheets-Sheet 2 L2 FIG. 5

L3 L4 L5 L6 L7 L8 FIG 4 TRANSVERSAL -SPHERICAL ABERRATlON l COMA ABERRATION ---26 --a73o O.2mm

L E 2mm 0 2mm 0 2% O SPHERICAL ABERRATION ASTGMAT'SM To noN SINUSOIDAL CONDlTION April 21, 1970 IKUO om 3,507,559

RETROFOCUS TYPE WIDE ANGLE OBJECTIVE LENS Filed Dec. 1, 1966 5 Sheets-Sheet 3 F I 6 TRANSVERSAL SPHERICAL ABERRATION COMA ABERRATION 26 *-33 SPHERICAL ABERRATION SINUSOIDAL couomow AST'GMAT'SM DISTORTION United States Patent 3,507,559 RETROFOCUS TYPE WIDE ANGLE OBJECTIVE LENS Ikuo Mori, Kawasaki-shi, Japan, assignor to Nippon Kogaku K.K., Tokyo, Japan, a corporation of Japan Filed Dec. 1, 1966, Ser. No. 598,249 Claims priority, application Japan, Dec. 7, 1965, 40/74,794 Int. Cl. G02b 9/00 US. Cl. 350-214 4 Claims ABSTRACT OF THE DISCLOSURE The present invention provides a retrofocus type wide angle objective comprising a front lens group of a dispersive system of which the refractive power is strength ened for shortening the distance between the dispersive system and the converging system. A member placed near the stop corrects the negative distortion, thereby obtaining a back focus longer than a definite length.

This invention relates to a retrofocus type wide angle objective lens.

Generally speaking, in retrofocus type lens system, when the focal length of the dispersive system of the front group is shortened, the back focus becomes longer and at the same time the lens size can be reduced. But in such a case, spherical aberration, distortion, and coma will be increased. It has hitherto been regarded to be very difiicult to correct them.

In accordance with the invention, there is provided a retrofocus type wide angle objective in which the diameter of the lenses of the front group are small in spite of the fact that the aperture ratio thereof is F:2.8 and the angle of view is over 75, and that the back focus is over 1.3 times larger than the focal length of the whole system (f), the objective lens being very small and light in weight,

at the same time, one in which the various kinds of aberrations are highly corrected. 7

The objective lens of the present invention comprises a front lens group or dispersive system, comprising two negative meniscus lenses L and L with convex surfaces thereof being directed toward the object and a rear lens gorup comprising a positive single lens L a positive doublet comprising two cemented lenses L and L a negative lens L and two positive meniscus lenses L L with concave surface thereof being directed towards the object, the resultant objective satisfying the conditions 4 5+ 1+ s) 'r-l' a) si and 1o 11 wherein d stands for the thickness of the center of a lens or for the air space between adjacent lenses; d being the air space between lenses L and L d the thickness of lens L d the thickness of lens L d the thickness of lens L d the thickness of lens L and ti being the air space between lenses L and L7- The present invention will now be described more in detail referring to the embodiments shown in the drawing, in which:

FIG. 1 is a cross section of Examples I and H of the optical system of the present invention;

FIG. 2 shows various aberration curves of Example I;

FIG. 3 is a cross section of Example III of the invention;

FIG. 4 shows various aberration curves of Example III;

FIG. 5 is a cross section of Example IV of the invention; and

FIG. 6 shows various aberration curves of Example IV,

Referring to FIG. 1 of the drawings, an embodiment of the present invention is illustrated in which the lens system comprises two lens groups. The front group comprises two negative meniscus lenses L and L having lens thicknesses d; and d respectively, the two lenses being separated by and air space d Lens L is separated by a comparatively large air space d, from the rear group of lenses comprising a positive lens L hav ng a thickness d separated by an air space d from a positive doublet comprising a positive lens L and a negative lens L cemented together, the lenses L and L having thicknesses d and d respectively. Separated from the cemented doublet by a diaphragm D and an air space d is a negative lens L having a thickness d separated by an air space d from. two positive meniscus lenses L and L having widths of d and d respectively and separated from each other by an air space 11 The radii of the various lens surfaces r through r are shown on the drawing.

The relationship of the lens thickness and the air space a, and d of the lens system disclosed is as (wherein d is the thickness of the center of a lens, or an axial distance between air separated lens surfaces).

In spite of the fact that the focal length of the dispersive system of the front group is comparatively shortened to about 1.06], the whole system being reduced in size, the spherical aberration and distortion generated in the dispersive system of the front group are corrected by the conditions (I) and (II) set forth above, the condition (I) being also effective to reduce the size of the lens system. If conditions of (I) and (II) were not satisfied, although it would be possible to obtain a comparatively long back focus, the lens of the rear group placed on the image side of the diaphragm could not correct the spherical aberration and the negative distortion caused by the front lens grouping. When the refractive indices n,

3 4 and thus the coma is corrected without deteriorating. The following are the examples of the present invenastigmatism. tion, and Seidels aberration coetficients thereof:

In general, a retrofocus type lens system has a draw back that the lens system itself and the aperture size of the front lens become large due to the following coni fS I ditions which are necessary for assuring a back focus a larger than a definite length: R 52 (1) distance between the leading lens and the stop 1s dl=5.59 m=1.6425 v =58.1 large- RFM'O d=13 29 (2) in order to correct the negative distortion, a mem- 1n R =128.85 her having a positive refractive power is included in the R4=7035 13:335 "P152041 "2:603 dispersive system. 4=31.47

For solving the above problem, it is proposed to Rpm; d=1748 n 160342 v 378 shorten the distance between the dispersive system and R6=625.0 k P the converging system and to correct the negative dis- 15 117:9, :035 tortion by a member placed as near to the stop as possible. d1=30.0 n4=1,717 v4=47.9 According to this proposal, in the present invention, the R8= 80'42 (18:4 55 715:150137 U :56 5 condition I is given for shortening the distance between Rv= 1.4 I 5 the leading or front lens and the stop. However, due to Rm= 64.0 condition I, the back focus becomes short, so that in order 20 d1o=14.0 m=1.7552 U0=27-5 to maintain the back focus to be longer than a definite R= 17657 =35 length, it is necessary to make the focal length of the dis- R12="300-0 persive system relatively short, i.e., as long as l.06f. P159623 F553 However, this results in the deterioration in various aber- 1a= 5 rations, particularly, spherical aberration and distortion. R= 14685 d=6 29 m=i-63854 F555 By the use of a radius of curvature of which the concave 1s= surface being directed to the incident light rays to the positive lens locating before the stop, the distortion is -f= corrected to some extent, while the spherical aberration is corrected by the condition II. In other words, the light rays projected parallel into the front lens receive a strong dispersive action by lenses L1 and L2 when they pass SEIDELS ABERRA'IION COEFFICIENTS IN EXAMPLE 1- through lens L and after passing, they still retain their dispersive state, which, however, shall receive converging Hz I113 IV; v, action by the surface R when they pass lenses L As described, the light rays receive reverse actions when they pass respective lenses, so that it is necessary to let the light rays pass through near to the center of radius of curvature. For this purpose, as shown in condition II, it is necessary to make large the central thickness of the lens giving converging action. By this condition, distortion is also corrected. The condition n n makes the above mentioned effect more effective, and at the same time is is preferably for the correction of chromatic aberrations. 1

As mentioned, conditions I and II given to the front lens group before the stop are not sufficient enough for the correction of distortion. For solving this, condition III is given. Namely, in general, the back focus and the distortion are changed in the opposite directions, and 5 when the central thickness d of the lens L is increased, EXAMPLE 11 it effectively works to shift both to the positive direc- 1:100 tion. However, it has the tendency to increase negative coma and the sagittal image surface is rapidly shifted to 111:1!)3, 15 the positive direction. In order to prevent this tendency R 72 1= 9 m=1.6516 vr=58-5 the space d is decreased. 2 37 d2=13. 29

When the condition I is not followed, the back focus can be increased, but at the same time negative distortion R4=60.73 dkass m 1'6223 02:53'1 is increased and it is not suitable for decreasing the total RFWM length of the lens system. 60 a5=17. 4s m=1. e727 v =32. a

When condition II is not followed, the back focus can RFJOM d =0.35 I be increased, but particularly, the spherical aberration R1=97.2 d 3112 172 503 is deteriorated so that it becomes impossible to assure R5=80.4 P uh a larger aperture ratio as in the present invention. R= 302.45 d8=4'55 When condition III is not followed, sagittal image surd@=17.5s face and coma aberration can be compensated from each am: 14,0 M=L72825 other, but distortion is deteriorated and the back focus RIF-17M d 5 is decreased so that it is not possible to obtain a long R12=234.26 1h back focus as in the present invention. Rl3= 62. 94 0 713 2 As a result of carrying out other conventional means dn'=0.35 for correcting aberrations after giving said conditions (I) d=6 29 m=L6516 5 through (III), it is possible to excellently correct vari- Rl5=93.7 a

ous aberrations in spite of the lens system being very small in size. B. f=l30.5

SEIDELS ABERRATION COEFFICIENTS IN EXAMPLE II I: III III; IV; V;

0. 099 0. 518 0. 426 0. 195 0. 406 0. 844 0. 762 0. 076 0. 294 0. 559 O. 380 0. 114 0. 001 0. 544 0. 544 0. 000 0. 530 0. 854 0, 310 0. 160 --0. 200 0. 666 0. 184 0. 226 1. 182 1. 148 0. 669 O. 135 0. 740 0. 638 0. 282 0. 068 0. 886 1. 524 0. 581 0. 310 2. 001 l. 840 1. 058 0. 205 l. 685 3. 574 l. 352 0. 888 0. 208 1. 190 0. 278 0. 610 0. 550 0. 878 0. 733 0. 096 0. 036 0. 302 0. 126 0. 300 0. 648 0. 592 0. 478 O. 043 0. 046 0. 131 0. 111 0. 164

FIG. 2 shows various aberration curves of example.

SEIDEL'S ABERRATION COEFFICIENTS IN EXAMPLE III FIG. 3 is the cross sectional view of optical system of Example 111. FIG. 4 shows various aberration curves thereof, and Example III is characterized in that it has no vignetting.

SEIDELS ABERRATION COEFFICIENTS IN FIG. 5 is the cross sectional view of the optical system of Example IV, and FIG. 6 shows various aberration curves thereof. It is inconvenient to use ordinary retrofocus lens system for large-sized single lens reflex cameras, such as, for example, of 6 cm. x 7 cm. film format, because the diameter of the front lens group is comparatively large. With the objectives of the present invention, that diameter can be reduced by making the values of d d and d smaller.

As mentioned above, in accordance with the present invention, in spite of the fact that the diameter of front group lenses is small, it is possible to obtain a small, lightweight, wide angle objective lens of retrofocus type in which the aperture ratio is F/2.8, the angle of view is over 75, and the back focus is over 1.3 times larger than the composite focal length of the lens system, and wherein various kinds of aberrations are well corrected.

What is claimed is:

1. A retrofocus type wide angle objective comprising a front lens groups or dispersive system including two negative meniscus lenses L and L with the covex surfaces thereof being directed toward the object, and a rear lens group comprising a positive single lens L a positive doublet of a positive lens L and a negative lens L cemented together, a negative lens L and two positive meniscus single lenses L L with the concave surfaces thereof being directed towards the object, the objective satisfying 7 8 and having the numerical data substantially as set forth wherein R R represent the radii of curvature of in the following table: the individual surfaces, d d represent the axial thickness of the individual elements and the axial lengths. f=100 of the air spaces between the components, n n represent refractive indices of the individual elements and RPM-52 (:559 m=L6425 01:58, v v represent Abbe numbers of the individual R1=54.0 elements. 31:12835 F1329 1 3. A retrofocus type wide angle objective comprising d1=3.s5 m=1.62041 vz=60.3 a front lens group or dispersive system including two (F3147 negative meniscus lenses L and L with the convex sur- R5=898.4 faces thereof being directed toward the object, and a rear RG42 "P150342 F318 lens group comprising a positive single lens L a positive d6=0.35 doublet of a positive lens L and a negative lens L 47:30,) m=m17 cemented together, a negative lens L and two positive Ra=-80.42 meniscus single lenses L L with the concave surfaces RD= 3OL4 "P150137 :565 thereof being directed towards the object, the objective R 0 a=1 satisfying the conditions Rl0 176 5'7 d1u=14.0 7H=L7552 U6=27-5 1P ri =3.5 2O 'z-la) 5 and R12- 00.0 dip m=m968 07:55.6 1o 11 (F035 and having the numerical data substantially as set forth RH=1468-5 in the following table:

d1i=a29 m=1aas54 8 55.5 I R1s=-100.8

wherein R R represent the radii of curvature of f=100 2w=75 F/2.8 the individual surfaces, d d represent the axial thickness of the individual elements and the axial lengths s of the air spaces between the components, n n RF 895 d1=5-594 represent refractive indices of the individual elements and dz=16.78 V V represent Abbe numbers of the individual (13:3 846 720:1 6041 02:603 elements. Ri=7o.35

2. A retrofocus type wide angle objective comprising a 125:9!" d*=31'469 front lens group or dispersive system including two negads=17.482 =1.57309 v;=42.7 tive meniscus lenses L and L with the covex surfaces (=0 35o thereof being directed toward the object, and a rear lens R1=97.167 group comprising a positive single lens L a positive dou- Ra= 78 67 11:29-72 "4:419 blet of a positive lens L and a negative lens L cemented 40 da=4.545 ns=1.50137 v =56.5 together, a negative lens L and two positive meniscus (1:17 832 single lenses L L with the concave surfaces thereof Rw=64.38 a being directed towards the object, the objective satisfying REM d1=14'755 "P135552 the conditions R 323 32 du=3.497 5 m d1z=7.692 m=1.e9es v =55.6 (d +d d and R"= 63'986 d1;=0.350

to 11 Rm 1900's d14=8.040 m=1.e425 v,=5s.1 Ru=98.927 and having the numerlcal data substantially as set forth in the following table: #131146 Rt=103. 15 Rt=54. 12 111:5 m=1'6516- wherein R R represents the radii of curvature d2=13.29 of the individual surfaces, d d represent the axial R=129'37 13:3 85 712:16223 02:531 thickness of the individual elements and the axial lengths R4=70.63 of the air spaces between the components, n n 36:979'0 represent refractive indices of the individual elements and dt=17.4s m=1. 6727 v3=32-2 60 v v represent Abbe numbers of the individual 46:0.35 elements. 1 R1=97.2 4. A retrofocus type wide angle objective comprising Rs=80.4 (17:3 12 72 a front lens group or dispersive system including two Razfiqm 45 s= s= s= negative meniscus lenses L and L with the convex sur- 55 faces thereof being directed toward the ob ect, and a rear RIF-6319 lens group comprising a positive single lens L a positive R,,= 1 6 Flam doublet of a positive lens L and a negative lens L cemented together, a negative lens L and two positive R1:=-234.26

meniscus single lenses L L w1th the concave surfaces R11=-6294 d 35 thereof being directed towards the object, the objective Ru=1073.4 satisfying the conditions 7 v ti 4=6. 29 1t3=1. 5516 05 58. 5 4 5+ 1'l7' a); 7-ia) 5; and B. f=l30.5

and having the numerical data substantially as set forth 1n the following table:

1!, =2. 00 n =1. 00241 v 50. a Rz= 50. 000

d3=2. 00 712 1. 60241 Ug=60.3 R1=63. 566

d =32. 71 n =1. 713 v =53.9 R -es. 214

dg==16.29 R 64. 286

d =17. o0 m=1. 7552 =27. 5 R =180. 0 45 d =9. 43 n =1. 713 0 :53. 9 R11= 59. 524

a 0. 43 m= 1. 62041 0 00. 3 R15= 7s. 310

wherein R R represents the radii of curvature of the individual surfaces, d d represent the axial thickness of the individual elements and the axial lengths of the air spaces between the components, n n represents refractive indices of the individual elements and PAUL R. GILLIAM, Primary Examiner 

